Abstract:Nano scale structures:
Much excitement has been generated in recent years by nano-science breakthroughs. A common characteristic of such developments has been the discovery of novel properties of materials of common composition but with characteristic dimensions in the nanometer range. The development of nano-structured materials has also inspired a renewed interest in shape-memory alloys (SMA’s), a class of materials known for the better part of a century. It is now well known that the favorable properties of SMA’s stem from their propensity for pervasive nano- and micro-scale twinning, a lattice-structure modulation associated with a displacive phase transformation.
Ordering of nanostructures:
Another feature of much present-day nano-science is found in phenomena of self-assembly, ordering and orientation of nano-structures, especially in the presence of a template or other symmetry-breaking boundary conditions. Such effects are extensions to the nano-scale of ordering effects well known in phase transitions, such as the growth of an ordered lattice from an amorphous melt in the presence of a crystalline seed, or the formation of ordered ferroelectric domains in the presence of applied electric fields. In the case of SMA’s, favorable orientation of the martensitic domains is achieved primarily by thermo-mechanical treatments such as drawing, annealing and cold-working, although other means are available as well.
Technological applications:
Transformations between the twinned phase (martensite) and the untwined phase (austenite) are accompanied by large mechanical effects known collectively as shape-memory effects (SME). Actuators based on these transformations are found to deliver a superior quantity of mechanical work per unit weight than competing technologies. Applications of SME are proliferating in such diverse areas such as medicine, aerospace and consumer products.
For many of these applications, the main technological competition is presented by small electric motors. At the heart of everything from DVD players to cell phones, these motors produce revenues in excess of $12B annually for motor manufacturers. The vast majority of them are based on the principles of electromagnetism discovered by Faraday over 170 years ago.
In spite of the age of this technology, powerful economic forces and entrenched design philosophies will make the adoption of new devices a slow process, but one with huge economic potential.
NanoMuscle, Inc. manufactures a new motor based on materials with nano-scale features. With orders for 10M units so far they are on their way to becoming the first commercially viable alternative to the small electric motor.